President Barack Obama promised Thursday during a closed-door meeting with Senate Democrats that he will not hesitate to use his veto power on hostile legislation sent from the Republican-led Congress, reported Politico.

Obama said at the Senate Democrats' summit in Baltimore that he would defend his agenda against any GOP attempt to undermine it, specifically promising to veto any legislation that would impose additional sanctions on Iran, as he believes it would impede ongoing nuclear negotiations.

The president insisted he would continue to be aggressive on issues such as immigration, housing, Cuba and medical leave, and even said he would issue more executive actions to implement his agenda, a move sure to anger Republicans already upset about Obama's unilateral use of power.

"I'm not going to spend the next two years on defense; I'm going to play offense," Obama said, two attendees told Politico.

While Obama has used his veto pen less than any other president in over 100 years, he made it clear that he would use it repeatedly during his remaining two years if necessary, including on the GOP-sponsored Keystone XL pipeline legislation.

"It was very direct and frank, but not in any way unfriendly or hostile," one senior senator told The New York Times. "Plainly, we have a path forward through administrative and executive actions, even if there are obstacles in the legislative process."

Several sources told Politico the meeting was more of a pep rally than a confrontation, and the president urged fellow Democrats to help him in his efforts. Obama spent most of the time at the Hilton hotel answering questions, though, according to Politico.

The first showdown between Obama and Republicans is likely to be over the Keystone pipeline bill expected to soon be debated. Following that, Republicans have indicated they will direct their attention to a bill designed to impose tougher sanctions on the Iranian economy, Fox News reported.

"We in the administration believe that, at this time, increasing sanctions would dramatically undermine our efforts to reach this shared goal" of reducing Iran's ability to produce nuclear weapons, Samantha Power, the U.S. ambassador to the United Nations, said earlier this week, according to Reuters.